Remove reaper from containerd daemon

This allows other packages and plugins to easily exec things without
racing with the reaper.

The reaper is mostly needed in the shim but can be removed in containerd
in favor of the `exec.Cmd` apis

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/containerd/config_linux.go

@@ -12,7 +12,6 @@ func defaultConfig() *server.Config {
 		GRPC: server.GRPCConfig{
 			Address: defaults.DefaultAddress,
 		},
-		NoSubreaper: false,
 		Debug: server.Debug{
 			Level:   "info",
 			Address: defaults.DefaultDebugAddress,

cmd/containerd/main_unix.go

@@ -11,7 +11,6 @@ import (
 	"golang.org/x/sys/unix"
 
 	"github.com/containerd/containerd/log"
-	"github.com/containerd/containerd/reaper"
 	"github.com/containerd/containerd/server"
 )
 
@@ -21,7 +20,6 @@ var handledSignals = []os.Signal{
 	unix.SIGTERM,
 	unix.SIGINT,
 	unix.SIGUSR1,
-	unix.SIGCHLD,
 	unix.SIGPIPE,
 }
 
@@ -36,10 +34,6 @@ func handleSignals(ctx context.Context, signals chan os.Signal, serverC chan *se
 			case s := <-signals:
 				log.G(ctx).WithField("signal", s).Debug("received signal")
 				switch s {
-				case unix.SIGCHLD:
-					if err := reaper.Reap(); err != nil {
-						log.G(ctx).WithError(err).Error("reap containerd processes")
-					}
 				case unix.SIGUSR1:
 					dumpStacks()
 				case unix.SIGPIPE: